1. Field of Invention
The present invention relates to electronic cameras that obtain an image signal by forming an object image on a solid-state image pick-up element that accumulates charge, such as, for example, a charge-coupled-device (CCD), and particularly to electronic cameras that shield the light supplied to the image pick-up element after charge accumulation.
2. Description of Related Art
Electronic cameras typically include a CCD as a solid-state image pick-up element. Charge accumulated on the CCD as image information is read, processed and recorded in a recording medium. Particularly when a frame transfer type CCD or a two-field reading type interline CCD is used, it is desirable to perform the reading of the charge in a state where the CCD is shaded from light. Furthermore, with other types of CCDs as well, it is desirable to read the charge when shielding the light to the CCD in order to seek a high quality image by positively preventing smear (a phenomenon where the charge that overflows from the CCD pixels flows into a transferring part, which causes vertical lines to appear in the image). For example, when an electronic camera is formed by incorporating a CCD into a single lens reflex camera that uses a silver halide film that has conventionally existed, it was normal to perform the shielding of the CCD using an existing focal plane shutter of the single lens reflex camera.
In an ordinary single lens reflex camera for use with silver halide film, a focal plane shutter has two sets of blade groups called a front curtain and a rear curtain, and the film is exposed by opening and closing these curtains at about the same time. Additionally, for example, there are cases when only the front curtain is closed before exposure (i.e, the rear curtain remains open), the front curtain is opened when the release button is depressed, and then exposure is completed by closing the rear curtain. Furthermore, as another type, there is a type in which the shielding is improved by closing both the front and rear curtains before exposure (this is called a double shielding shutter), the rear curtain is opened prior to exposure, exposure begins by opening the front curtain, and, subsequently, exposure is completed by closing the rear curtain. In either type, by accurately changing the time between the front curtain being opened and the rear curtain being closed, a plurality of shutter speeds (exposure times) are realized.
However, if a shutter is to be used for shielding of the CCD only, one set of shutter blades is sufficient, and high accuracy is not required for driving. In the conventional single lens reflex electronic camera, because the relatively large focal plane type shutter for silver halide film, with two sets of shutter blades, is used as-is for the shielding member of the CCD, this can be a disadvantage in terms of space. Additionally, there is waste in driving the shutter blade (waste in terms of time and energy consumption).